Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.41   11.169%   $259.4796   $259.48   $259.50   $259.50  
  Purchase #2 $238.40   6.515%   $253.9318   $253.93   $253.95   $253.90  
  Purchase #3 $106.95   3.662%   $110.8665   $110.87   $110.85   $110.90  
  Purchase #4 $108.83   7.176%   $116.6396   $116.64   $116.65   $116.60  
  Purchase #5 $161.87   4.506%   $169.1639   $169.16   $169.15   $169.20  
  Purchase #6 $57.72   12.596%   $64.9904   $64.99   $65.00   $65.00  
  Purchase #7 $46.33   7.573%   $49.8386   $49.84   $49.85   $49.80  
  7 purchase totals = $953.51       $1,024.9104   $1,024.91   $1,024.95   $1,024.90